Method of fabrication of striped magnetoresistive (SMR) and dual stripe magnetoresistive (DSMR) heads with anti-parallel exchange configuration

ABSTRACT

A method for forming a longitudinally magnetically biased dual stripe magnetoresistive (DSMR) sensor element comprises forming a first patterned magnetoresistive (MR) layer. Contact the opposite ends of the patterned magnetoresistive (MR) layer with a first pair of stacks defining a track width of the first magnetoresistive (MR) layer, each of the stacks including a first Anti-Ferro-Magnetic (AFM) layer and a first lead layer. Then anneal the device in the presence of a longitudinal external magnetic field. Next, form a second patterned magnetoresistive (MR) layer above the previous structure. Contact the opposite ends of the second patterned magnetoresistive (MR) layer with a second pair of stacks defining a second track width of the second patterned magnetoresistive (MR) layer. Each of the second pair of stacks includes spacer layer composed of a metal, a Ferro-Magnetic (FM) layer, a second Anti-Ferro-Magnetic (AFM) layer and a second lead layer. Then anneal the device in the presence of a second longitudinal external magnetic field.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to Striped Magnetoresistive (SMR) headsand Dual Stripe Magnetoresistive (DSMR) heads and more particularly tomethods of manufacturing of exchange biasing configurations therefor, aswell as devices manufactured by such methods.

[0003] 2. Description of Related Art

[0004] As the continuous trend in magnetic recording requires increasedarea density, track widths of magnetic recording heads are beingreduced. Commonly assigned U.S. patent application No. 09/182,775, filedOct. 30, 1998 of Yimin Guo et al. for “Anti-Parallel LongitudinalPatterned Exchange Biased Dual Stripe Magnetoresistive (DSMR) SensorElement and Method for Fabrication Thereof” describes a narrow trackwidth DSMR head with dual sensors. The head, which increases signalamplitude is stabilized by anti-parallel biasing, i.e. with biasingwhich is parallel, but in the opposite directed or oriented. In such abiasing scheme, the magnetic centers of dual sensors self-align eachother.

[0005] Accordingly, no track-offsetting is needed as disclosed incommonly assigned U.S. Pat. No. 5,783,460 of Han et al. for “Method ofMaking Self-Aligned Dual Stripe MagnetoResistive (DSMR) Head for HighDensity Recording” which shows a DSMR process using a lift off stencilto form a patterned dielectric layer edge. To achieve this quiescentbiasing scheme, one can produce both sensors with Anti-ParallelEXchange-biasing (APEX) by means of exchange coupling betweenAnti-Ferro-Magnetic (AFM) and Ferro-Magnetic (FM) material.

[0006] U.S. Pat. No. 5,408,377 of Gurney et al. for “MagnetoresistiveSensor with Ferromagnetic Sensing Layer ” shows a Ruthenium (Ru) AFMcoupling film in a spin valve sensor.

[0007] U.S. Pat. No. 5,644,456 of Smith et al. for “Magnetically CappedDual Magnetoresistive Reproduce Head” shows a cap layer in a DSMR thatbreaks exchange coupling between the magnetically permeable layer and MRelements.

[0008] U.S. Pat. No. 5,684,658 of Shi et al. for “High Track DensityDual Stripe Magnetoresistive (DMSR) Head” shows a DSMR having first andsecond anti-Ferro-Magnetic longitudinal biasing layers.

[0009] U.S. Pat. No. 5,731,936 of Lee et al. for “Magnetoresistive (MR)Sensor with Coefficient Enhancing that Promotes Thermal Stability”provides chromium based spacer layers for an MR layer of NiCr or NiFeCrcompositions in place of Ta spacers to avoid a reported problem ofdegrading the magnetic moment of the MR stripe when high heat at theinterface between the Ta spacer layer and the Permalloy (MR stripe)causing interdiffusion therebetween.

[0010] See Parkin, “Systematic Variation of the Strength and OscillationPeriod of Indirect Magnetic Exchange Coupling through the 3d. 4d and 5dTransition Metals”, Physical Review Letters Vol. 67, No. 25, pp.3598-3601 (Dec. 16, 1991)

[0011] U.S. Pat. No. 5,766,780 of Huang et al. for “Reversed Order NiMnExchange Biasing for Dual Magnetoresistive Heads” teaches a DSMR with aMo layer as the conductor/seed layer on an alumina base coat. A NiMnexchange bias layer is formed on the Mo layer. A NiFe MR sensor layer isformed on the surface of the NiMn exchange bias layer.

SUMMARY OF THE INVENTION

[0012] This invention teaches a Ruthenium/Ferro-Magnetic/AFM three layerstructure to replace an AFM in a sensor in an MR or DSMR. In the case ofa DSMR, when one magnetically aligns both AFM in the same direction, thebiasing direction of the MR sensor under the ruthenium will beanti-parallel to the other one. A key element of the invention is the Ruspacer that shows increased coupling strength.

[0013] In accordance with this invention a method is provided forforming a longitudinally magnetically biased dual stripemagnetoresistive (DSMR) sensor element comprises forming a firstpatterned magnetoresistive (MR) layer. Contact the opposite ends of thepatterned magnetoresistive (MR) layer with a first pair of stacksdefining a track width of the first magnetoresistive (MR) layer, each ofthe stacks including a first Anti-Ferro-Magnetic (AFM) layer and a firstlead layer. Then anneal the device in the presence of a longitudinalexternal magnetic field. Next, form a second patterned magnetoresistive(MR) layer above the previous structure. Contact the opposite ends ofthe second patterned magnetoresistive (MR) layer with a second pair ofstacks defining a second track width of the second patternedmagnetoresistive (MR) layer. Each of the second pair of stacks includesspacer layer composed of a metal, a Ferro-Magnetic (FM) layer, a secondAnti-Ferro-Magnetic (AFM) layer and a second lead layer. Then anneal thedevice in the presence of a second longitudinal external magnetic field.

[0014] In accordance with another aspect of this invention, alongitudinally magnetically biased dual stripe magnetoresistive (DSMR)sensor element is provided including a first patterned magnetoresistive(MR) layer. There are a pair of opposite ends of the first patterned MRlayer being in contact with a first pair of stacks defining a firsttrack width of the patterned MR layer. Each of the stacks includes afirst AFM layer and a first lead layer. The device has a firstlongitudinal magnetic field bias in the first AFM layer. There is asecond patterned MR layer contacted at its opposite ends by a secondpair of stacks defining a second track width of the second patterned MRlayer. Each of the second pair of stacks includes a spacer layercomposed of a metal, a Ferro-Magnetic (FM) layer, a second AFM layer anda second lead layer. The device has a second longitudinal magnetic fieldbias in the second AFM layer. Preferably, the spacer layer is composedof a metal selected from the group consisting of ruthenium (Ru), rhodium(Rh), copper (Cu) and chromium (Cr). It is also preferred that theFerro-Magnetic layers are composed of a metal selected from the groupconsisting of NiFe, Co, Fe, NiCo and CoFe. Moreover, it is preferredthat the AFM layers are composed of a metal selected from the groupconsisting of IrMn, NiMn, PtMn, PdPtMn and FeMn.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The foregoing and other aspects and advantages of this inventionare explained and described below with reference to the accompanyingdrawings, in which:

[0016]FIG. 1 illustrates an application of an exchange biasing structureof a Ferro-Magnetic/spacer/Ferro-Magnetic/Anti-Ferro-Magnetic(MR/SP/FM/AFM) for biasing a single MR sensor longitudinally inaccordance with this invention.

[0017] FIGS. 2A-2D show a method of employing the method of thisinvention in a Dual Stripe Magneto-Resistive (DSMR) head application, inwhich one can replace the bias structure of one of sensors by themulti-layer structure of this invention as illustrated by FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0018] In accordance with this invention, to fabricate an Anti-ParallelEXchange-biasing (APEX) head, two Anti-Ferro-Magnetic (AFM) layers witha distinct difference in blocking temperatures are selected. We findthat by annealing at two different temperatures, one achieves an APEXstate in a Dual Stripe Magneto-Resistive (DSMR) head. Another approachis to use the same AFM material in the biasing layers. The AFM layer ofthe first MR sensor is annealed in a desired first direction ofmagnetization. We also find that the AFM layer of the second MR sensoris consequently annealed in the opposite direction without degrading theexchange magnetic field magnitude and direction of first AFM layer ofthe first MR sensor.

[0019] We find, in addition, that APEX heads manufactured by thesemethods require a magnetic initialization process to set sensors back toAPEX state. Further in accordance with this invention, the longitudinalswitch threshold magnetic field for two MR sensors can be determined.Our specific recipe of longitudinal magnetic field provides a sequencefor tailoring the exchange magnetic field, coercivity and annealingconditions.

[0020] In a GMR device, a strong interlayer coupling which is known asAnti-Parallel Ferro-Magnetic Interlayer (APFI) coupling, can be used ina sandwiched structure of Ferro-Magnetic/spacer/Ferro-Magnetic layers.When depositing an AFM layer onto such a sandwiched structure, a strongAFM layer magnetization pins the magnetization of its neighboringmagnetic layer. The bottom Ferro-Magnetic layer is in an APFI couplingstate.

[0021] In the embodiment of this invention shown in FIG. 1, net magneticflux is determined from the difference of magnetic moment of bottom andtop Ferro-Magnetic layers which comprise the magnetoresistive layer MRon the bottom and Ferro-Magnetic layers FL/FR on the top.

[0022]FIG. 1 illustrates an application of an exchange biasing structureof a Ferro-Magnetic/spacer/Ferro-Magnetic/Anti-Ferro-Magnetic(MR/SP/FM/AFM) for biasing a single MR sensor longitudinally inaccordance with this invention. The device of FIG. 1 includes asubstrate SUB upon which is formed a shield layer SHL upon which a firstnon-magnetic spacer layer NMS is formed. The magnetoresistive sensor MRis formed on the first non-magnetic spacer layer NMS. Refill layers RFLand RFR are formed on the surface of the left and right ends ofmagnetoresistive sensor MR and a set of second non-magnetic spacerlayers SL and SR are formed on the surfaces of the refill layers RFL andRFR above the magnetoresistive sensor MR. Above the second non-magneticspacer layers SL and SR are formed a set of Ferro-Magnetic layers FL andFR upon which are formed exchange biasing Anti-Ferro-Magnetic (AFM)layers AL and AR which overlie the ends of layers FL and FR. In turnleads LL, and LR have been formed over the AFM layers AL and ARrespectively.

[0023] The exchange biasing AFM layers AL and AR are shown afterannealing in the presence of an externally applied magnetic field Hαshown in phantom (since it is no longer present) which has produced alongitudinal biasing magnetic field from left to right in theFerro-Magnetic layers FL and FR with reversely directed, pinned magneticfields in the Ferro-Magnetic layers FL and FR above the ends ofmagnetoresistive sensor MR. The magnetic fields of the Ferro-Magnetic,magnetoresistive sensor layer MR causes a resultant matching andopposite, magnetic field from right to left in the magnetoresistivesensor MR.

[0024] In practice, the net magnetic flux of the structure is needed tostabilize and bias the magnetoresistive sensor MR. The net magnetic fluxis determined from the difference of magnetic moment of bottomFerro-Magnetic magnetoresistive sensor MR and the top Ferro-Magneticlayers FL and FR.

[0025] FIGS. 2A-2D show a method of employing the method of thisinvention in a Dual Stripe MR (DSMR) head application, in which one canreplace the bias structure of one of sensors by the multi-layerstructure of this invention as illustrated by FIG. 1. When we reset thebias direction, both sensors MR1 and MR2 will be automatically biased inanti-parallel directions as seen in FIG. 2D. This structure can alsogreatly simplify the annealing process and can also greatly simplify theinitialization process.

[0026] The Anti-Parallel (AP) initialization becomes simple, since bothAnti-Parallel Magnetizations (APM) are in a unique direction. Aftercompleting all the necessary thermal cycles for wafer fabrication, thewafer will be annealed in a high longitudinal magnetic field which isslightly larger than shield saturation (the value is depend on shieldmaterial and design). The sensor magnetization can be reset accordingly.

Process Steps

[0027]FIG. 2A shows a device 20 being manufactured in accordance withthe method of this invention. A substrate SUB composed of a materialsuch as a ceramic, e.g. alumina (Al₂O₃), titanium carbide (TiC), hasbeen coated with a shield layer SHL preferably composed of aferromagnetic material such as Permalloy (NiFe, 80:20). Upon the shieldlayer a spacer layer SP is formed composed of a non-magnetic material,e.g. alumina (Al₂O₃), silicon oxide (SiO₂) or silicon nitride (Si₃N₄).Upon the spacer layer SP a first magnetoresistive sensor layer MR1 isformed composed of a Ferro-Magnetic material such as Permalloy (NiFe,80:20), Co, Fe, NiCo, or CoFe.

[0028] Next, on the left and right ends of the magnetoresistive sensorMR1 a pair of stacks are formed on the top surface of magnetoresistivesensor MR1 with a track width TW1 formed therebetween, conventionalprocessing techniques such as a lift-off process.

[0029] In the stack on the left, there are three layers starting withthe refill layer RF1 (RL1 in FIG. 2D) formed of NiFe/80:20 on thesurface of magnetoresistive sensor MR1 followed by the left AFM layerALL preferably formed of a material selected from the group consistingof IrMn, NiMn, PtMn, PdPtMn and FeMn. On top of the left AMF layer ALLis the left lead line LLL, preferably formed of copper.

[0030] In the stack on the right, there are three layers starting withthe refill layer RR1 formed of NiFe/80:20 on the surface of the rightend of the magnetoresistive sensor MR1 followed by the right AFM layerARL preferably formed of a material selected from the group consistingof IrMn, NiMn, PtMn, PdPtMn and FeMn. On top of the right AMF layer ARLis the right lead line LLR, preferably formed of copper.

[0031]FIG. 2B shows the device of FIG. 2A after having been annealed inthe presence of an externally applied magnetic field H1 shown in phantom(since it is no longer present) which has produced a longitudinalbiasing magnetic field from left to right in AFM layers ALL and ARLproducing a magnetic field from right to left in the sensor MR1.

[0032]FIG. 2C shows the device of FIG. 2B after formation of theremaining layers of the DSMR but prior to annealing of the AFM layersthereof. First an intermediate dielectric layer ISD is formed composedof a non-magnetic dielectric material, e.g. alumina (Al₂O₃), siliconoxide (SiO₂) or silicon nitride (Si₃N₄).

[0033] Next, a second magnetoresistive sensor layer MR2 is formedcomposed of a Ferro-Magnetic material such as Permalloy (NiFe, 80:20),Co, Fe, NiCo, or CoFe.

[0034] Next, on the left and right ends of the MR sensor MR2 an upperpair of stacks are formed on the top surface of Magneto-Resistive sensorMR2 with a track width TW2 formed therebetween, conventional processingtechniques such as a lift-off process.

[0035] In the upper stack on the left, there are five layers startingwith the upper left refill layer RFU formed of NiFe/80:20 on the surfaceof magnetoresistive sensor MR2, followed by the upper left spacer layerSRL formed preferably of ruthenium (Ru) or at least one of rhenium (Rh),copper (Cu) or chromium (Cr). Above the upper left spacer layer SLU isformed the upper left Ferro-Magnetic layer FLU preferably composed of aFerro-Magnetic material such as Permalloy (NiFe, 80:20), Co, Fe, NiCo,or CoFe.

[0036] Next follows the upper left AFM layer ALU preferably formed of amaterial selected from the group consisting of IrMn, NiMn, PtMn, PdPtMnand FeMn. On top of the upper left AMF layer ALU is the upper left leadline LLU, preferably formed of gold.

[0037] In the upper stack on the right, there are five layers startingwith the upper right refill layer RRU formed of NiFe on the surface ofthe right end of the magnetoresistive sensor MR2, followed by the upperright spacer layer SRU formed preferably of ruthenium (Ru) or at leastone of rhodium (Rh), copper (Cu) or chromium (Cr).

[0038] Next follows upper right Ferro-Magnetic layer FRU preferablycomposed of a Ferro-Magnetic material such as Permalloy (NiFe, 80:20),Co, Fe, NiCo, or CoFe. Upon layer FRU is formed exchange biasingAnti-Ferro-Magnetic (AFM) layers ALU, preferably formed of a materialselected from the group consisting of IrMn, NiMn, PtMn, PdPtMn and FeMn.On top of the right AMF layer ARU is the right lead line LLR, preferablyformed of gold.

[0039]FIG. 2D shows the device of FIG. 2C after having been annealed inthe presence of an externally applied magnetic field H2 shown in phantom(since it is no longer present) which has produced a longitudinalbiasing magnetic field from left to right in the Ferro-Magnetic layerslayers FLU and FRU in the same direction producing a magnetic field fromright to left with reversely directed, pinned magnetic fields from rightto left in the sensor MR2 and from right to left in the sensor MR1.

SUMMARY

[0040] In the sandwiched structure, there are coupling forces betweenthe magnetic layers that try to align their magnetization directions tobe either parallel (P) or anti-parallel (AP). With increasingthicknesses of the spacers SL and SR, the P and AP will be alternated.The most pronounced coupling effect is observed when Ru was used as thespacer layer SL and SR. In this case, the coupling strength can reach alevel ten (10) times stronger than that provided by a copper (Cu) spaceror other noble metals. The Ru layer thickness can be selected so thatthe bottom layer will be in an APF1 (Anti-Parallel Ferro-MagneticInterlayer) coupling state.

[0041] For a DSMR head dual MR layer structure, fabrication of the AFMlayer in one of the two MR sensors is replaced by Ru/Ferro-Magnetic/AFMthree layers. When we magnetically align two AFM layers in the samedirection, the biasing direction of the sensor under the Ru layer willbe automatically anti-parallel to that the other one. Substitution forthe Ru layer can be made by metals selected from Rh, Cu and Ir. TheFerro-Magnetic film can be made of a material selected from a metal suchas Co or Fe or alloys such as NiFe, NiCo and CoFe. The AFM layer can becomposed of an alloy such as IrMn, NiMn, PtMn, PdPtMn and FeMn, etc.

[0042] While this invention has been described in terms of the abovespecific embodiment(s), those skilled in the art will recognize that theinvention can be practiced with modifications within the spirit andscope of the appended claims, i.e. that changes can be made in form anddetail, without departing from the spirit and scope of the invention.Accordingly, all such changes come within the purview of the presentinvention and the invention encompasses the subject matter of the claimswhich follow.

Having thus described the invention, what is claimed as new anddesirable to be secured by Letters Patent is as follows:
 1. A method forforming a longitudinally magnetically biased stripe magnetoresistivesensor element comprising: forming a first patterned magnetoresistive(MR) layer, contacting a pair of opposite ends of said patternedmagnetoresistive (MR) layer with a pair of stacks defining a track widthof said patterned magnetoresistive (MR) layer, each of said stacksincluding as follows: a spacer layer composed of a metal, aFerro-Magnetic (FM) layer, an Anti-Ferro-Magnetic (AFM) layer and a leadlayer, and annealing said device in the presence of a longitudinalexternal magnetic field.
 2. A method in accordance with claim 1 whereinsaid spacer layer is composed of a metal selected from the groupconsisting of ruthenium (Ru), rhodium (Rh), copper (Cu) and chromium(Cr).
 3. A method in accordance with claim 1 wherein said Ferro-Magneticlayer is composed of a metal selected from the group consisting of NiFe,Co, Fe, NiCo and CoFe.
 4. A method in accordance with claim 1 whereinsaid AFM layer is composed of a metal selected from the group consistingof IrMn, NiMn, PtMn, PdPtMn and FeMn.
 5. A method in accordance withclaim 1 wherein: said spacer layer is composed of a metal selected fromthe group consisting of ruthenium (Ru), rhodium (Rh), copper (Cu) andchromium (Cr), and said Ferro-Magnetic layer is composed of a metalselected from the group consisting of NiFe, Co, Fe, NiCo and CoFe.
 6. Amethod in accordance with claim 1 wherein: said spacer layer is composedof a metal selected from the group consisting of ruthenium (Ru) rhodium(Rh), copper (Cu) and chromium (Cr), said Ferro-Magnetic layer iscomposed of a metal selected from the group consisting of NiFe, Co, Fe,NiCo and CoFe, and said AFM layer is composed of a metal selected fromthe group consisting of IrMn, NiMn, PtMn, PdPtMn and FeMn.
 7. A methodfor forming a longitudinally magnetically biased dual stripemagnetoresistive (DSMR) sensor element comprising: forming a firstpatterned magnetoresistive (MR) layer, contacting a pair of oppositeends of said patterned magnetoresistive (MR) layer with a first pair ofstacks defining a track width of said patterned magnetoresistive (MR)layer, each of said stacks including as follows: a firstAnti-Ferro-Magnetic (AFM) layer and a first lead layer, and annealingsaid device in the presence of a longitudinal external magnetic field,forming a second patterned magnetoresistive (MR) layer, contacting apair of opposite ends of said second patterned magnetoresistive (MR)layer with a second pair of stacks defining a second track width of saidsecond patterned magnetoresistive (MR) layer, each of said second pairof stacks including as follows: a spacer layer composed of a metal, aFerro-Magnetic (FM) layer, a second Anti-Ferro-Magnetic (AFM) layer anda second lead layer, and annealing said device in the presence of asecond longitudinal external magnetic field.
 8. A method in accordancewith claim 7 wherein said spacer layer is composed of a metal selectedfrom the group consisting of ruthenium (Ru), rhodium (Rh), copper (Cu)and chromium (Cr).
 9. A method in accordance with claim 7 wherein saidFerro-Magnetic layers are composed of a metal selected from the groupconsisting of NiFe, Co, Fe, NiCo and CoFe.
 10. A method in accordancewith claim 7 wherein said AFM layers are composed of a metal selectedfrom the group consisting of IrMn, NiMn, PtMn, PdPtMn and FeMn.
 11. Amethod in accordance with claim 7 wherein: said spacer layer is composedof a metal selected from the group consisting of ruthenium (Ru), rhodium(Rh), copper (Cu) and chromium (Cr), and said Ferro-Magnetic layers arecomposed of a metal selected from the group consisting of NiFe, Co, Fe,NiCo and CoFe.
 12. A method in accordance with claim 7 wherein: saidspacer layer is composed of a metal selected from the group consistingof ruthenium (Ru), rhodium (Rh), copper (Cu) and chromium (Cr), saidFerro-Magnetic layers are composed of a metal selected from the groupconsisting of NiFe, Co, Fe, NiCo and CoFe, and said AFM layers arecomposed of a metal selected from the group consisting of IrMn, NiMn,PtMn, PdPtMn and FeMn.
 13. A longitudinally magnetically biased stripemagnetoresistive sensor element comprising: a first patternedmagnetoresistive (MR) layer, a pair of opposite ends of said firstpatterned magnetoresistive (MR) layer contacted with a pair of stacksdefining a first track width of said first patterned magnetoresistive(MR) layer, each of said stacks including as follows: a spacer layercomposed of a metal, a Ferro-Magnetic (FM) layer, an Anti-Ferro-Magnetic(AFM) layer a lead layer, and said device having a longitudinal magneticbias.
 14. A device in accordance with claim 13 wherein said spacer layeris composed of a metal selected from the group consisting of ruthenium(Ru), rhodium (Rh), copper (Cu) and chromium (Cr).
 15. A device inaccordance with claim 13 wherein said Ferro-Magnetic layer is composedof a metal selected from the group consisting of NiFe, Co, Fe, NiCo andCoFe.
 16. A device in accordance with claim 13 wherein said AFM layer iscomposed of a metal selected from the group consisting of IrMn, NiMn,PtMn, PdPtMn and FeMn.
 17. A device in accordance with claim 13 wherein:said spacer layer is composed of a metal selected from the groupconsisting of ruthenium (Ru), rhodium (Rh), copper (Cu) and chromium(Cr), and said Ferro-Magnetic layer is composed of a metal selected fromthe group consisting of NiFe, Co, Fe, NiCo and CoFe.
 18. A device inaccordance with claim 13 wherein: said spacer layer is composed of ametal selected from the group consisting of ruthenium (Ru) rhodium (Rh),copper (Cu) and chromium (Cr), said Ferro-Magnetic layer is composed ofa metal selected from the group consisting of NiFe, Co, Fe, NiCo andCoFe, and said AFM layer is composed of a metal selected from the groupconsisting of IrMn, NiMn, PtMn, PdPtMn and FeMn.
 19. A device for alongitudinally magnetically biased dual stripe magnetoresistive (DSMR)sensor element comprising: a first patterned magnetoresistive (MR)layer, a pair of opposite ends of said first patterned MR layer being incontact with a first pair of stacks defining a first track width of saidpatterned MR layer, each of said stacks including as follows: a firstAnti-Ferro-Magnetic (AFM) layer and a first lead layer, and said devicehaving a first longitudinal magnetic field bias in said first AFM layer,a second patterned MR layer, contacting a pair of opposite ends of saidsecond patterned MR layer with a second pair of stacks defining a secondtrack width of said second patterned MR layer, each of said second pairof stacks including as follows: a spacer layer composed of a metal, aFerro-Magnetic (FM) layer, a second AFM layer and a second lead layer,and said device having a second longitudinal magnetic field bias in saidsecond AFM layer.
 20. A device in accordance with claim 19 wherein saidspacer layer is composed of a metal selected from the group consistingof ruthenium (Ru), rhodium (Rh), copper (Cu) and chromium (Cr).
 21. Adevice in accordance with claim 19 wherein said Ferro-Magnetic layersare composed of a metal selected from the group consisting of NiFe, Co,Fe, NiCo and CoFe.
 22. A device in accordance with claim 19 wherein saidAFM layers are composed of a metal selected from the group consisting ofIrMn, NiMn, PtMn, PdPtMn and FeMn.
 23. A device in accordance with claim19 wherein: said spacer layer is composed of a metal selected from thegroup consisting of ruthenium (Ru), rhodium (Rh), copper (Cu) andchromium (Cr), and said Ferro-Magnetic layers are composed of a metalselected from the group consisting of NiFe, Co, Fe, NiCo and CoFe.
 24. Adevice in accordance with claim 19 wherein: said spacer layer iscomposed of a metal selected from the group consisting of ruthenium(Ru), rhodium (Rh), copper (Cu) and chromium (Cr), said Ferro-Magneticlayers are composed of a metal selected from the group consisting ofNiFe, Co, Fe, NiCo and CoFe, and said AFM layers are composed of a metalselected from the group consisting of IrMn, NiMn, PtMn, PdPtMn and FeMn.